''Firearms are the second leading cause of death in the United States for ages 15 to 34, with motor vehicles in first place and cancer a distant third,'' said Susan P. Baker, a professor in the department of health policy at Johns Hopkins School of Hygiene and Public Health.

For people in the 30-to-54 age group, the rate of firearm deaths is even worse, tying with motor vehicle accidents for first place, she reported in the American Journal of Public Health.

''As with deaths from other causes, the risk of death from firearms is not equally shared by the population,'' she said.

The risk of accidentally being killed by a gun is 10 times higher in low-income areas than in high-income neighborhoods, Baker said.

Elderly white males have the highest risk of killing themselves with a gun. A black person's risk of being murdered with a gun is six times that of a white person, she said. Guns are used in two of every three murders.

One black out of 40 between the ages of 20 and 44 will be murdered by a gun, she said. Firearm homicide rates for blacks in large cities are more than 10 times the national average.

''We often hear that 'Guns don't kill people, people kill people,''' said Baker.

But the wide availability of guns in this country contributes to the high death rate, especially in deaths resulting from impromptu arguments and fights, she said. Half of U.S. households have a firearm and one-fifth of them are handguns.

Two-thirds of the nearly 8,000 deaths in 1981 involving arguments and brawls were caused by guns, said Baker.

''These deaths would largely be replaced by nonfatal injuries if a gun were not handy,'' she said. ''Thus, a far more appropriate generality would be that 'People without guns injure people; guns kill people.' ''

Baker said that lawsuits against manufacturers, based on their having introduced unreasonably hazardous products into the stream of commerce, may eventually help to stem the tide of handgun production and sales.

Other approaches to reducing firearm injuries include development of less lethal handgun ammunition and design of firearms so they cannot be discharged easily by young children, or accidentally, she said.

''Given the magnitude of this public health problem, the time is past due to attack it on many fronts,'' Baker said.